Automatic regulation of the power factor in electric furnaces



Jan. 8, 1929.

D. F. CAMPBELL ET AL.

AUTOMATIC nneumnon 0F m POWER FACTOR m ELECTRIC FURNACES Filed Jan. 4, 1928 2 sheets-sheet "1 w fiazfzz 5622 Jan. 8, 1929.

D. F. CAMPBELL ET AL AUTOMATIC REGULATION OF THE POWER FACTOR IN ELECTRIC FURNACES Filed Jan. 1928 2 Sheets-Sheet 2 Mb n b M .mq I

. Patented Jan. 8, 1929.

UNITED STATES 1,698,581 PATENT OFFICE.

DONALD FRASER CAMPBELL AND GEORGE EDWARD TAYLOR, OF LONDON, ENGLAND.

AUTOMATIC REGULATION THE POWER FACTOR IN ELECTRIC FURNACES.

Application filed January 4, 1928, Serial No. 244,494, and in Great Britain liecember 20, 192 6.

The invention relates to the regulation of the power factorin electrical circuits such as the metal or material to be heated, which forms the secondary circuit, is contained.

In electric circuits of this type any change in the impedance of the secondary circuit causes a change in the impedance of the priwmary circuit. It'will, therefore, be obvious that the impedance of the inductor coil will vary according to the nature of the metal placed in the container,its resistance, which varies as the temperature alters, and on the size and form of the particles of the material. Owing to the inherent characteristics of this type of heating, the power factor of the above circuit is very low, and therefore for commercial use it is necessary to correct the and condenser are in series with each other;

the voltages across the coil and thecondenser respectively will vary according to the 1mpedance and current, in the circuits.

According to the invention in: order to' maintain the power factor at the required.

value, two solenoids or other suitable magneto-electric devices are energized either by the current or voltage in the inductor coil and condenser circuit respectively.

The energized coils may, for example, act in opposite directions on a plunger, so that when the currents in the coils are equal a pointer attached to the plunger is at thezero of an indicating scale, and moves to one side or other of the 'scale as the force due to one or other of the currents predominates.

Alternatively, the currents may act inde power factor so as to bring it as near unity as reduced to maintain the required value.

Owing to the change ofimpedanceof the pendently on two plungers, pointers on which are arranged to rotate independently about the same axis, so that any ine uality in the currents is indicated by the divergence of co 'the pointers, which may be differently col-.

oured.

The capacity may be adjusted by hand in orderto bring the single pointer to its zero indication or the two polnters into coinci- 65 dence and, consequently, to adjust the power factor to the required value.

In a preferred form the adjustment is made automatically. For this purpose a plunger energized by the opposing currents is adapted to make and-break circuits to which contac'tor switches are connected by which condenserunits can be inserted in, or removed from, thecircuit.

In the accompanying drawings which represent diagrammatically circuit arrangements according to the invention- Figs. 1 and 2 show the capacity connected respectively in parallel and in series with the mam energizing coil, and y Fig. 3 is an example of a circuit in which the capacity is automatically increased or power factor at the Referring to Fig. 1, G is a generator or other source of alternating current, the main energizing coil of the primary circuit of the furnace is shown at E and 10 ,10 In represent condensers which can be inserted or removed as required by closing or opening switches 8 .s', s. The condenser k is shown as connected in the circuit.

A, A are the electromagnetic devices energized respectively by current flowing in permanently the circuits of the coil E and of the conden- .sers.

Indicators are assumed to be attached to the moving members of the devices A A shown in Fig. 1 or the devices A, A shown in Fig. 3, and according to the indicators the switches 8 a, 8 etc. are opened or closed either manually as in Fig. 1, or automatically. as in- Fig. 3. As previously explained, the indicatin devices A A may be combined in a sing e instrument,as shown in Fig. 3, a plunger or other moving member being ener gized by the differential action of the currents flowin respectively in the condenser circuit and t e main energizing coil.

In Fi 2 the condensers are connected in series. with the coil E and the indicating instruments V V? are energized by the 'voltages across the coil E and the condensers rc-" Y spectively.

Referring to Fig. 3, the electromagnetic coils A 'A? are similar to the electromagnetic devices A A shown in Fig. 1. B

and B are current transformers in the circuit of the coil E and the capacity respectively. C and C are resistances shunting the coils B B I The plungers 72 b are connected together and pivoted at (Z and are so arranged that if the current in the coil A is greater than the current in the coil A, the plunger 6 is drawn upwards and a switch 6 is closed. This implies that the power factor is below the predetermined value and. requires for its adjustment that the-capacity should be increased.

. Current flows from the positive pole of a 1. source B of direct current over lead 1, conent of the switch 6 is provided over leads 1,

10, 11-, switch i closed by the armature s coil 7", lead 5, contacts 6 and 7, leads 8 and 9 to the negative pole of the battery B.

Armature s also closes a switch 3' but this switch j has a delayed'action, so that it is only closed if the contacts of the switch e are maintained closed for a interval of time.

The continued closure of switch e for the time necessary to close switch 7' implies that .the capacity requires to be further inpredetermined creased and a circuit is now established over lead 1, contacts 2 and 3, switch e lead 12,

switch 3', lead 13, coil 7", lead 14, closed switch 9 leads 15. and 9 to the negative pole.

of the batteryB. Coil) attracts its armature 8 against the resistance of spring k and inserts the condenser 70 in parallel with k and 70 Armature s closes switch 2? and a delayed action switch 9' and opens switch Z Switch i provides a locking circuit for co'il f over closed switches 2' and g and over j after a predetermined time connects up coil f to battery B if switch e 'is still closed.

Assuming that the condensers in, W, k areconnected in parallel with k and that the impedance of coil E is reduced, so that the capacity is too great to obtain the predetermined value of the power factor, the plunger 6 will close switch e and plunger 6 will open switch a. j

Current now flows from positive pole of battery B, over lead 1, switch 6 leads 16 and 17, magnetizing coil m leads 18 and 9 to the condenser 70 in parallel negative pole of the battery. The energized v coil'mf opens switch g and thereby interrupts the locking circuit of coil 7, the main circuit of which was interrupted when contacts 2 and 3 were opened by 6 Armature 8 is released by spring k and condenser 70 is out off from the circuit; Z is also closed after a predetermined time.

If 6 still remains closed, coil m is ener gized by current from positive pole of battery B, lead 1, switch 6 lead 16, closed switch Z lead 19, coila h leads 20 and 9 to negative pole of battery.

Capacity is now out out by the interruption of its locking circuit at 9 v Similarly,.if e is still closed after 7: is cut out, coil m is energized over closed switches Z Z and condenser k is cut out.

'While only three removable capacities or condenser units 70 40 are shown in Figs. 1-3,

it is obvious that their number can be increased largely according to therequirements of the installation.

The circuit arrangements shown can be easily modified for the case in which the capacityis in series, instead of in parallel, with the main energizing coils.

Having thus de'scribedthe nature of our said invention and the best'means. we know of carrying the same into practical effect, we c aim 1. A device for approximately maintain ing the power factor of a load circuit of. an

alternating current electric furnace comprising a source of alternating current, a circuit including inductive and condensive elements connected to said source, means for introducing said condensive elements into and removing them from said circuit, and electro-mag-' netic indicating means embodying windings coupled respectively to said inductive and condensive elements and energized in accordance with the electrical conditions existing therein. I v s a 2. A device for approximately maintaining the power factor of a load circuit of an alternating current electric furnace comprising a source of alternating current, a circuit including inductive and condensive elements connected to said source, means for introducing said condensive elements into and rem0V-. ing them from said circuit, and electro-magnetic means for controlling the introduction and removal of the condensive elements with respect to said circuit embodying opposed windings coupled respectively to the mductive and condensive elements and energized respectively in accordance with the electrical conditions existing therein.

3. -,A device for approximately mainta ning the power factor of a load circuit. of a'n alc ternating'current electric furnace comprlsmg a source of alternating current, inductive and condensive branched c1rcu1ts therefrom, an

inductor in the inductive circuit, condensers adapted to be introduced into the condensive circuit, transformers having primaries rea source of alternating current, inductive and condensive branched circuits therefrom, an inductor in the inductivecircuit, condensers in the condensive circuit adapted to be inserted'therein or withdrawn'therefrom, transformers having primaries respectively in the two circuits, sets of switches adapted, respectively, one set progressively to insert and the other progressively to withdraw condensers,

electro-megnetic means for operating the switches alternatively. having op osed windings-energized respectively by t e two secondaries of said transformers and depending, for the selection, upon which winding has the predominant energization, and electro magnetic means and connections for causing the closing of the switches of one set to insert and of the other set to withdraw condensers.

5. Ina device for maintaining a substantially predetermined power factor in the supply circuit for an alternating current furnace, a source'of alternating current supply, an inductor circuit connected therewith, conden sive power factor correction means cooperative with "theinductor circuit, transformers I whose primaries are responsive to the current flow through the inductor circuit and condensive correction means respectively, opposed electrd-magnetic means ener ized, respectively, by the secondaries of t e transformers, an indicator controlled by said electro-magnetic means whereby the relation of the currents through theinductor circuit and correction means 'may be determined, and means for varymg sald correctlon means accordlng to the determinations of the'mdlcator.

6. In a device for maintaining a substantially predetermined power factor in the sup-.

ply circuit for an alternating current furnace, a source of alternating current supply, an inductor circuit connected therewith, condensive power factor cbrrection means including a plurality of condensers cooperative with the inductor circuit, transformers whose primaries are responsive to the current flow through the inductor circuit and condensers, respectively, opposed electro-magnetic connectlons form the secondaries of the transformers, electric switches controlled by the preponderance of energization of one or the other of said opposed electro-Ihagnetic connections by one or' the other of the two sceondaries, cir cuits closed alternatively by said switches,

and electro-magnetic operating connections controlled by said alternative y closed circuits whereby the number of condensers in circuit is increased or diminished according to which switch is closed.-

In testimony whereof we have signed our names to this s ecification.

DONAL FRASER CAMPBELL. GEORGE EDWARD TAYLOR. 

